家兔脑组织复电阻抗频率特性及其等效电路模型

目的：研究大脑组织的复电阻抗频率特性,分析缺血对大脑组织复电阻抗频率特性的影响,构建大脑组织的复电阻抗等效电路模型。方法：利用频响分析仪(1255B,英国Solartron公司),二电极测量法,对12只家兔正常、缺血状态大脑组织复电阻抗频率特性进行离体测量,脑缺血方法采用的是颈总动脉结扎法,等效电路模型分析采用阻抗分析软件(Zplot 2．1,英国Solartron公司),还经过脑组织病理学常规染色(HE染色)对脑缺血进行了验证。结果：在缺血脑损伤发生后,脑组织复电阻抗实部、虚部均明显增大,电阻率变化率受频率影响较小,但脑组织复电阻抗虚部频率特性未呈现出单峰走势,经软件分析得到了脑组织的复电阻抗等效电路模型。讨论：脑组织复电阻抗实部、虚部和电阻率变化率均可以作为成像变量;其复电阻抗等效电路模型显示整体脑组织的等效电路模型构成比较复杂,并非传统的生物组织三元件等效电路模型,在进一步的研究中应设法对各组织分别进行测量。     

乳腺电阻抗扫描的频率特性初步分析

利用电阻抗扫描技术,对正常人体乳腺进行多个激励频率的测量,用于研究在其他条件相同的情况下,频率改变对测量所得的复电导的影响.获得了同一个体以及不同个体的正常乳腺的电阻抗扫描数据的频率特性曲线,分析了其一般特征,并对比了个体之间的差异情况.同时,还获得了乳头组织的频率特性曲线,并与其周围正常组织对比,揭示了这两种不同性质组织的频率特性具有显著区别.     

基于体外阻抗测量的恶性胶质瘤介电特性

目的研究脑胶质瘤生物电阻抗特性,探索出恶性胶质瘤组织与正常脑组织的特征性电参数,为区分恶性胶质瘤与正常脑组织提供依据。方法基于四电极法阻抗测量设计了一种体外阻抗测量传感器,利用普林斯顿阻抗分析仪Versa STAT3对10例裸鼠脑胶质瘤和脑组织进行阻抗测量,并对20Hz~250 k Hz范围内阻抗频谱特性曲线进行定量分析;结合生物阻抗谱理论,建立体外脑胶质瘤等效电路模型,并利用ZSimp Win对等效阻抗电路进行拟合仿真,以探讨脑胶质瘤在阻抗电路中的特性。结果胶质瘤的阻抗模值在20 Hz~250 k Hz范围内随频率的增大而减小,幅值曲线在200 Hz和50 k Hz附近各存在一个斜坡,这两个斜坡的斜度都小于对应的正常鼠脑组织的斜度。10组裸鼠体外实验中,胶质瘤和脑组织的虚部-实部图中有两个时间环节,可以用两个时间常数的等效电路代替,并且电路元件中的参数R1对于胶质瘤和脑组织差异明显。结论体外鼠脑胶质瘤与正常脑组织可以用阻抗特性曲线的斜坡值进行定量区别。此外,等效电路电参数中的R1也可以作为一个区分胶质瘤和脑组织的指标,这为临床检测和区分胶质瘤组织开拓了新的研究思路。     

骨质疏松症诊断技术与电阻抗特性分析

骨质疏松症已成为老龄化社会面临的重要疾病之一。概述了骨质疏松症现代物理诊断的三大主流技术及其它诊断方法,介绍了生物组织电阻抗频率特性测量技术的原理、骨组织复电阻抗测量分析方法和在骨质疏松症早期诊断和监测的应用前景。     

体外人脑胶质瘤电阻抗特性及等效电路

目的 研究人脑胶质瘤的电阻抗特性并建立其等效电路,可为进一步区分人脑胶质瘤和正常脑组织的阻抗特性差异提供依据.方法 利用英国Solartron公司的阻抗分析仪（1260）,采用四端法,在10 Hz ～ 10 MHz范围内,对4例体外人胶质瘤组织进行电阻抗测量.通过分析其频率特性并结合已有的人脑组织的等效电路,建立了体外胶质瘤的等效电路,利用阻抗分析软件Z-VIEW对其进行仿真.结果 体外人脑胶质瘤的阻抗模值在10 Hz～10 MHz范围内随频率的增大而下降,相位角在该范围内随频率的增大而增大.体外人脑胶质瘤组织在10 kHz ～ 10 MHz范围内电阻抗实部比较稳定,其中在10Hz～ 10 kHz范围内,实部随频率的增大而减小.电阻抗虚部在20 kHz ～ 10 MHz范围内较稳定,而在10Hz ～ 20 kHz范围内,虚部随频率增大而增大.样本的等效电路仿真曲线与实际曲线相比较,等效电路模型能较好地反映体外人脑胶质瘤的电阻抗特性.结论 体外人脑胶质瘤与已知的正常脑组织的电阻抗特性及等效电路差别明显,这为探索生物电阻抗技术应用于区别胶质瘤与正常脑组织的临床应用提供了研究基础.     

家兔红细胞阻抗谱的实验和等效电路拟合研究

目的：研究家兔红细胞阻抗谱并建立RC等效电路模型参数。方法：在0．01MHz-100MHz频率范围，使用Agilent 4294A阻抗分析仪测量了家兔红细胞交流阻抗，通过Bode图、Nyquist图、Nicols图、Randles图的曲线拟合分析，比较三个RC等效电路模型的拟合残差。结果：（1）家兔红细胞阻抗谱的第一特征频率fc1=2．5MHz，第二特征频率fc2=5．25MHz；（2）等效电路模型，模型3的拟合误差小于模型1和模型2；（3）等效的单个红细胞膜电容约为0．458／μF／cm^2。结论：家兔红细胞阻抗谱表现出两个特征频率，其等效电路模型以模型3形式更为合理。     

在体兔脑组织电阻抗频率特性测量及EIT初步成像

通过频响分析仪，二电极法，对10只家兔大脑缺血前后的脑阻抗频率特性进行在体测量，再尝试利用16电极EIT成像系统，对兔脑阻抗的一变化进行初步的动态成像实验，缺血模型采用的是颈总动脉结扎法，并经过单侧颈总动脉大脑供血区域染色实验。对缺血进行了验证，结果显示，在缺血脑损伤发生后，脑阻抗明显增大，在10Hz以下脑阻抗变化率可达75％,1KHz-1MHz频率范围脑阻抗变化率约为15％且比较稳定，理论上完全满足成像要求，而且脑阻抗变化率可以作为一个成像变量；初步的动态成像结果显示，脑组织供血变化一侧与其电阻率变化位置相一致，从而进一步证明利用EIT技术对脑功能变化进行检测，成像是完全可行的。     

动物组织复电阻抗谱随离体时间的变化

建立基于四电极法的测量系统，测量了犬和兔部分离体组织的复阻抗谱，观察了部分动物组织复电阻抗谱随离体时间而发生的变化，结果发现，随着动物组织离体时婚的延长，其复阻抗谱发生显著变化：1、低频段电阻显著增加；2、复阻抗谱的虚部增加(容性成份增加)；3、特征频率降低。结合动物组织离体后发生的组织、细胞水平的变化，我们认为：动物组织复电阻抗谱随离体时间的变化应该与组织细胞内液、细胞外液的离子成份变化相关，同时应该与细胞膜活性相关。     

几种乳腺疾病的电阻抗扫描的频率特性

利用电阻抗扫描技术,研究人体乳腺在疾病状态下电导参数随激励频率的变化规律,为进一步的乳腺疾病检查打下基础。获得了浸润性导管癌、瘤样增生和乳腺腺病等三种乳腺疾病的电导参数的频率特性曲线,并与病变周围正常组织进行了对比,可以得出病变组织具有与正常组织不同的频率特性,而且上述三种不同种类疾病的频率特性也各有差异。因此提示可以根据频率特性的特征,来辨别病变的种类。     

基于EIT技术颅内电阻抗特性分析

电阻抗断层成像技术（EIT）是一种基于生物组织电学特性的成像技术。本研究基于EIT技术对二维四层同心圆头模型和基于MRI图片构造的脑电二维真实头模型的电阻抗特性进行了分析，给出了头部组织电导率参数变化对求解区域场内及头皮表面电位分布的影响，得出了有实际意义的结论，为实现颅内EIT逆问题求解和阻抗成像及脑内电特性的深入研究奠定了基础。     

Microfluidic device for cell capture and impedance measurement

This work presents a microfluidic device to capture physically single cells within microstructures inside a channel and to measure the impedance of a single HeLa cell (human cervical epithelioid carcinoma) using impedance spectroscopy. The device includes a glass substrate with electrodes and a PDMS channel with micro pillars. The commercial software CFD–ACE+ is used to study the flow of the microstructures in the channel. According to simulation results, the probability of cell capture by three micro pillars is about 10%. An equivalent circuit model of the device is established and fits closely to the experimental results. The circuit can be modeled electrically as cell impedance in parallel with dielectric capacitance and in series with a pair of electrode resistors. The system is operated at low frequency between 1 and 100 kHz. In this study, experiments show that the HeLa cell is successfully captured by the micro pillars and its impedance is measured by impedance spectroscopy. The magnitude of the HeLa cell impedance declines at all operation voltages with frequency because the HeLa cell is capacitive. Additionally, increasing the operation voltage reduces the magnitude of the HeLa cell because a strong electric field may promote the exchange of ions between the cytoplasm and the isotonic solution. Below an operating voltage of 0.9 V, the system impedance response is characteristic of a parallel circuit at under 30 kHz and of a series circuit at between 30 and 100 kHz. The phase of the HeLa cell impedance is characteristic of a series circuit when the operation voltage exceeds 0.8 V because the cell impedance becomes significant.     

The Application of Bode Analysis to Skin Impedance

A method is described for analyzing skin impedance data and applied to the determination of a steady-state electrical model for intact human skin. An algorithm is presented for the analytical procedure, Bode analysis, and a sample impedance function is obtained. Bode plots are employed to synthesize a passive equivalent circuit from sample measurements of “black box” skin impedance magnitude and phase angle, and representative values for the circuit elements are presented.     

Specific impedance of canine blood

The specific impedance of canine erythrocytes suspended in plasma was measured in the frequency range from 5 kHz to 1 MHz in samples from three animals in the hematocrit range from zero to packed cells at a temperature of 39°C; measurements were made with a conductivity cell using four electrodes and a current density of 21 μA/cm². With the use of impedance spectroscopy, data were fitted to an equivalent circuit model; model parameters in turn were fitted as functions of hematocrit. The resultant model can be used to predict specific impedance (real and reactive components) as a function of hematocrit and frequency over a frequency range from 5 kHz to 1 MHz and a hematocrit range from 0 to 80. Over a normal range of hematocrits and at frequencies less than 100 kHz., the current is almost exclusively confined to the plasma, and the specific impedance is nearly equal to the real component; however, at higher frequencies, the complex nature of specific impedance becomes important.     

Analysis for the change of skin impedance

Skin impedance, for various reasons, changes in a very complex fashion. The range of change of skin impedance is determined experimentally and analysed theoretically. The equivalent circuit of the skin impedance, the theoretical relationships among the variable parameters in this circuit, and the impedance space are proposed as powerful concepts for the analysis of impedance changes. The experimental examples are practically analysed and can well be understood. A theoretical foundation taking into consideration the mechanism of the change has been established in this paper.     

血液三元件阻抗的计算方法

根据血液的三元件电阻抗模型，以双频率复阻抗信息为已知量，详细介绍了三元件值的推导过程，建立了一套可获得三元件基础量和搏动量的完整表达式，为血液电阻抗特性的研究提供了一种新的三元件法。     

Non-linear electrical properties of skin in the low frequency range

This paper describes the non-linear electrical properties of the skin during the passage of a sinusoidal current from the standpoint of the constant-current method. The non-linearity occurs in the current dependency of the skin impedance and in Lissajous figures. It exhibits both rapid and slow variations. The concept of a non-linear impedance and its equivalent circuit are introduced for a sinusoidal voltage. With regard to the current dependency of the impedance it can be said that both the starting point and the degree of the dependency vary with frequency and impedance. The nonlinearity is more apparent with a larger current, a lower frequency, and a higher impedance. with an increasing current, the ionic conductance increases and the polarisation admittance decreases. Lissajous figures are formed when the voltage is distorted notably from the sinusoidal wave form. Detailed investigations are undertaken for the elliptic figures, third harmonics, rectification, and breakdown of the skin appearing with a decrease of the frequency and increase of the current. Finally, the special mechanism of the ionic conduction in the keratin layer is indicated as one of the causes for non-linearity.     

Specific impedance of canine blood

The specific impedance of canine erythrocytes suspended in plasma was measured in the frequency range from 5 kHz to 1 MHz in samples from three animals in the hematocrit range from zero to packed cells at a temperature of 39°C; measurements were made with a conductivity cell using four electrodes and a current density of 21 μA/cm². With the use of impedance spectroscopy, data were fitted to an equivalent circuit model; model parameters in turn were fitted as functions of hematocrit. The resultant model can be used to predict specific impedance (real and reactive components) as a function of hematocrit and frequency over a frequency range from 5 kHz to 1 MHz and a hematocrit range from 0 to 80. Over a normal range of hematocrits and at frequencies less than 100 kHz., the current is almost exclusively confined to the plasma, and the specific impedance is nearly equal to the real component; however, at higher frequencies, the complex nature of specific impedance becomes important.